Kolesnikova T D, Balantaeva M N, Pokholkova G V, Antonenko O V, Zhimulev I F
Institute of Molecular and Cellular Biology of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia Novosibirsk State University, Novosibirsk, Russia.
Novosibirsk State University, Novosibirsk, Russia.
Vavilovskii Zhurnal Genet Selektsii. 2025 Jun;29(3):414-422. doi: 10.18699/vjgb-25-44.
The achaete-scute complex (AS-C) is a locus approximately 90 kbp in length, containing multiple enhancers. The local expression of the achaete and scute genes in proneural clusters of Drosophila melanogaster imaginal discs results in the formation of a well-defined pattern of macrochaetae in adult flies. A wide variety of easily analyzed phenotypes, along with the direct connection between individual regulatory elements and the development of specific setae make this locus a classic model in developmental genetics. One classic AS-C allele is sc8, which arose as a result of the In(1) sc8 inversion. One breakpoint of this inversion lies between the ac and sc genes, while the second is in the pericentromeric heterochromatin of chromosome X, within satellite block 1.688. The heterochromatic position of the breakpoint raised the question of whether position effect variegation contributes to the disruption of normal locus function in the In(1)sc8 flies. However, conflicting results were obtained. Previously, we found that a secondary inversion, In(1)19EHet, arose spontaneously in one of the stocks of the In(1)sc8 BDSC line, transferring most of the heterochromatin from the ac gene to the 19E region of the X chromosome. Here, we demonstrate that the In(1)19EHet inversion leads to complete rescue of the number of posterior supraalar (PSA) and partial rescue of the number of dorsocentral (DC) macrochaetes observed in the original In(1)sc8 line. The same rescue of the macrochaetes pattern was observed when the In(1)sc8 inversion was introduced into a strain with the Su(var)3-906 position effect modifier. Combining the inversion with the Rif11 mutation, a conserved factor determining late replication and underreplication, does not restore the normal pattern of bristles. Our data indicate that the phenotype of flies carrying the In(1) sc8 inversion, associated with a disturbance in bristle development, is determined by the effect of heterochromatin on the distal part of the locus. This model can be used to test the influence of various factors on the position effect variegation caused by heterochromatin. Another phenotypic manifestation of In(1)sc8, a decreased proportion of males in the offspring, was independent of the proximity of the distal part of AS-C to heterochromatin and was not affected by the Rif11 mutation.
achaete - scute复合体（AS - C）是一个长度约为90千碱基对的基因座，包含多个增强子。果蝇成虫盘原神经簇中achaete和scute基因的局部表达导致成年果蝇形成定义明确的大刚毛模式。各种各样易于分析的表型，以及单个调控元件与特定刚毛发育之间的直接联系，使这个基因座成为发育遗传学中的经典模型。一个经典的AS - C等位基因是sc8，它是由In(1)sc8倒位产生的。这个倒位的一个断点位于ac和sc基因之间，而另一个在X染色体的着丝粒周围异染色质中，在卫星块1.688内。断点的异染色质位置引发了位置效应斑驳是否导致In(1)sc8果蝇正常基因座功能破坏的问题。然而，得到了相互矛盾的结果。之前，我们发现一个二级倒位In(1)19EHet在In(1)sc8 BDSC品系的一个品系中自发产生，将大部分异染色质从ac基因转移到X染色体的19E区域。在这里，我们证明In(1)19EHet倒位导致原In(1)sc8品系中观察到的后上腋（PSA）刚毛数量完全恢复，背中（DC）大刚毛数量部分恢复。当将In(1)sc8倒位引入带有Su(var)3 - 906位置效应修饰因子的品系时，观察到相同的刚毛模式恢复。将倒位与Rif11突变（一个决定晚期复制和复制不足的保守因子）结合，不能恢复正常的刚毛模式。我们的数据表明，携带In(1)sc8倒位的果蝇的表型与刚毛发育紊乱有关，是由异染色质对基因座远端部分的影响决定的。这个模型可用于测试各种因素对异染色质引起的位置效应斑驳的影响。In(1)sc8的另一个表型表现，即后代中雄性比例降低，与AS - C远端部分与异染色质的接近程度无关，并且不受Rif11突变的影响。
